This invention relates to an antithrombogenic, highly elastic polyurethane compound suitable for biomedical materials. More particularly, this invention relates to an antithrombogenic, highly elastic polyurethane compound excellent in biocompatibility and mechanical properties, which is produced by the reaction of a diisocyanate and a diamine upon a polyoxyethylene-polyoxypropylene-block copolyether having hydroxyl terminal groups.
The biomedical materials, particularly those for use in devices exposed to contact with blood such as, for example, catheters, A-V shunts for artificial kidneys, artificial lungs, blood bypass tubes, pumping chambers for artificial hearts, and balloon pumping materials, are required to possess blood compatibility and biocompatibility and mechanical properties such as flexibility, elasticity, durability, and wet toughness.
Generally, synthetic polymers stable under physiological environment are conveniently used as elastic biomedical materials. Unfortunately, silicone and plasticized polyvinyl chloride, which have the above-mentioned properties, are insufficient in antithrombogenicity. This fact constitutes itself a serious drawback for biomedical materials which are to be used at positions exposed to contact with blood. To overcome the drawback, there have been developed various devices aimed at vesting these synthetic polymeric compounds with an antithrombogenicity.
It has been known to impart an antithrombogenicity to polymers by blending an anticoagulant such as heparin or urokinase into such compounds or chemically combining such compounds with the anticoagulant. This impartment of the antithrombogenicity, however, is accomplished at the expense of mechanical properties. The antithrombogenicity thus imparted has a disadvantage that it is wholly or partially lost when the compounds are subjected to a treatment for thermal sterilization.
Certain polyurethane compounds have been demonstrated to possess an antithrombogenicity. Some of them have already been commercialized. They are represented by the following general formula. ##STR2## (wherein, R denotes an aromatic group). Although they excel in strength and elasticity, their hydrophilicity and antithrombogenicity are not quite satisfactory. [Literature: J. W. Boretos et al., J. Biomed. Mater. Res., 2, 121 (1968), 9, 327(1975)]
A blockcopolymer of a polyurethane compound and silicone resin has also been demonstrated to possess an antithrombogenicity. [Product marketed under trademark designation of Avcothane, Literature: E. Nylas et al., J. Biomed. Mater. Res. Symp., 3, 97, 129(1972)]
This copolymer has a disadvantage that it can be produced only by a highly complicated process, is readily torn, and tends to adsorb lipids.
A polyurethane compound having a polyoxyethylene block as a soft segment has been reported. [Literature: C. T. Chen et al., J. Appl. Polm. Sci., 16, 2105(1972), Kiyotaka Furusawa et al., Kobunshi Ronbunshu, 34, 309(1977)]. Although this compound manifests an antithrombogenicity, it exhibits elasticity and other mechanical properties at very low levels and readily undergoes hydrolysis. Thus, it finds little practical utility. A product obtained by grafting a hydroxyl-containing compound to a polyurethane compound has been demonstrated to possess an antithrombogenicity. It has unsatisfactory mechanical strength for practical use. [Literature: S. D. Bruck, J. Biomed. Mater. Res. Symp., 8, 1 (1977), B. Jansen et al., J. Polym. Sci., Symp. 66, 465(1979)].
All the efforts made to date have yielded results which suggest that the incorporation of hydrophilic groups to improve various polyurethane compounds in their antithrombogenicity result in the decrease of their mechanical properties. Thus, it is thought difficult to obtain compounds suitable for practical use.
An object of this invention is to provide a novel polyurethane compound which retains intact the antithrombogenicity possessed inherently by polyurethane compounds or exhibits this property to an enhanced extent, excels in elasticity, resistance to hydrolysis, wet toughness and other mechanical properties, and excellent biocompatibility.